Retry initialize operations
Retry initialize operations

When starting up RabbitMQ on a small container with CPU limits enabled,
we often run in a race condition when attempting to create a new user in
RabbitMQ. The output returns:

```
Creating user 'user'
Error: {noproc,{gen_server2,call,
                            [worker_pool,{next_free,<5457.110.0>},infinity]}}
```

We can't really know in advance whether RabbitMQ is ready or not, so
rather than guess by looking at `rabbitmqctl -q status`, we'll retry all
our initialization operations for about a minute.

aptible/docker-rabbitmq,aptible/docker-rabbitmq,aptible/docker-rabbitmq,aptible/docker-rabbitmq